Better: Hard. Leonard was more complete, as many have mentioned, but peak Ali was a physical freak to go along with his boxing IQ and will to win. I would have to go with Ali, because in his prime he was always able to impose his game plan on the opponent. Leonard didn't manage to against Duran in their first fight. A bit harsh perhaps, but since they're so close that's the difference maker for me. Greater: Again a close call. Both have great top wins, but Leonard's best four trumps Ali's best four, I'd say. But I also value consistency highly, and Ali more or less cleaned out two generations of contenders while you at best can give Leonard one. He aslo defended his undisputed title many, many more times (Leonard only did once, right?) and I put a lot of value in defences, since the challenger often is going to be more motivated than the champion. It's a different kind of pressure compared to taking on a huge challenge which no one expects you to pull off, and Ali excelled in both aspects where as Leonard really only excelled in one of them. Therefore I go with Ali here as well.